Butter fingers

Butter fingers

Pencil and paperOnline interactive
Overview
Using this Resource
Connecting to the Curriculum
Marking Student Responses
Working with Students
Further Resources
This task is about explaining calculation errors.
Doug was using a calculator to do his maths but he made lots of mistakes. He always got the first number right but got the operation or the second number wrong. In each case explain the mistake he made. The first one has been done for you.
 
Question:
Doug's answer:
Mistake:
7,123 + 8,641
14 764

Question 1Change answer

a) Question: 89 – ⁻23
  Doug's answer: 66
 
Mistake:

Question 1Change answer

b) Question: 17 × 56
  Doug's answer: 0.303571428
 
Mistake:

Question 1Change answer

c) Question: 35 × 25%
  Doug's answer: 875
 
Mistake:

Question 1Change answer

d) Question: 7.25 + 5.602
  Doug's answer: 12.87
 
 
Mistake:
 
 
 
Task administration: 
This task can be completed with pencil and paper or online (with NO auto-marking).
Level:
5
Curriculum info: 
Maths, Number and Algebra, Number Strategies
Keywords: 
estimation
Description of task: 
Students explain errors in calculations that include all operations, decimal values, and percentages.
Learning Progression Frameworks
This resource can provide evidence of learning associated with
Additive thinking
Multiplicative thinking, sets 8-9
within the Mathematics Learning Progressions Frameworks.
Read more about the Learning Progressions Frameworks.
Answers/responses: 
 

Y10 (11/1999)
a) Any 1 of:

•   He subtracted 23 (instead of ⁻23).
•   He added ⁻23 (instead of subtracting it).
•   He pressed the subtraction key twice (instead
     of pressing the negative sign button).

 moderate
b) He divided (instead of multiplying). moderate
c) Any 1 of:

•   He multiplied by 25 (instead of 0.25 or 25%).
•   He pressed = (instead of the percent key).
•   He didn't divide the answer by 100 to find the
     percentage.

 moderate
d) He added 5.62 (instead of 5.602). difficult
Diagnostic and formative information: 
  Common errors
a) He subtracted ⁻23 instead of 23.
c) He didn't put in the % sign.
d) He rounded to .85 rather than .87.